Thermostat



W. A. SAU L April 28, 1942.

THERMOSTAT Filed Sept. 14, 1940 2 Sheets-Sheet l W. A. SAUL THERMOSTAT April 28, 1942.

Filed Sept. 14, 1940 2 Sheets-Sheet 2 FIGIO.

Patented Apr. 28, 1942 THERMOSTAT Waldo Af. Saul, Lexington, Mass., assignor to Metals & Controls Corporation,

Attleboro,

Mass., a corporation oi' Massachusetts Application September 14, 1940, Serial No. 356,717 20 Claims; (Cl. 20o-138) This invention relates to thermostats, and more particularly to thermostats containing composite thermostatic elements wound in the form of a helix such as shown and described in Parsons Patent 2,121,259.

Among the objects of the invention may be noted the provision of a simple and compact thermostat embodying a thermostatic element such as shown in said Parsons. patent, which operates'as a rate of change thermostat, sensitive to rates of change of temperature; the provision of such a thermostat which in certain useful respects is not affected by ambient temperature changes; and the provision of a thermostat of the class described which operates with a snap action, thereby eliminating or decreasing arcing between contacts. Other objects will be in part obvious and in part pointed out hereinafter.

The invention accordingly comprises the elements and combination of elements, features of construction, and arrangement of parts which will be exemplified in the structures hereinafter described, and the scope of the application of which will be indicated in the following claims.

In the accompanying drawings in which are illustrated several exemplary embodiments of the invention,

Fig. l is a plan view of one type of thermostat made in accordance with the present invention;

Fig. 2 is a cross-section taken along the line y2--2 of Fig. 1;

Fig. 3 is an end elevation of the construction shown in Fig. 1;

Fig. 4 is a plan view of an alternative embodiment of the invention;

` Fig. 5 is a cross-section taken along the line 5-5 in Fig. 4; I

Fig. 6 is a left-end elevation of the embodiment shown in Fig. 4;

Fig. 7 isa cross-section of an alternate embodiment of the invention;

Fig. 8 isa cross-section of the Fis. 7 embodiment in a different operating position;

Fig. 9 is a top plan view ot the embodiment shown in Figures 7 and 8.

Fig. 10 is a partial cross-section of an alternative form of the Fig. 7 embodiment o1' the invention;

Fig. 11 is a partial cross-section of still another embodiment of the Fig. 7 form of the invention; and,

Fig. 12 is a section taken along the line 12-12 in Fig. 11.

The present invention refers to composite thermostat elements of the type shown and described in Parsons Patent No. 2,121,259, and to rateofchange thermostats embodying these composite elements.

cylinder, located close to the may be made by iirst winding a narrow strip of composite thermostatic metal, such as bimetal, into a helical form having a relatively small diameter. V second or major helical form of relatively large diameter, thus forming 'a compound or double helical thermostatic element, or a peripherally continuous operating member, as described in said Parsons Patent 2,121,259. The compositemetal or bimetal helix or spring so formed will expand or contract lengthwise with change of temperature. The amount of movement for a given temperature change is controlled by the relation between the various dimensions of the element and the direction of movement is controlled by the direction of winding of the two helices, and the relative positions of the high and low expansion sides of the bmetal.

Referring to the drawings, a thermostatic element is shown at I, embodying a helix as described above, shown at 2. The thermostat l is formed with a shield 3 in the form of a half outer portion of the helix 2. The shield is so constructed that it does not readily transmit heat or has a relatively large heat mass and therefore keeps the surrounded portion of the helix from rising in temperature as fast as the-outer side of helix, for quick temperature changes, but does allow all portions to change slowly in temperature with slow changes in ambient temperature. The helix operates a movable contact 4, which cooperates with a stationary contact 5, to open or close a circuit. The helix itself is supported at the opposite end, as shownv at 6, by attaching it to the main thermostat body l.

The thermostat is shown in Figures 1 and 2 as being in the open position. Gradual changes in the ambient temperature will not close the contacts, since the helix will expand and contract in a horizontal direction, rather than downwardly to bring the contact 4 into operative association with the stationary contact 5. However, a sudden rise in ambient temperature will ailect the more exposed portion of the helix at l, for example, more quickly than the portion U, which is closely tted to the shield 3. As a result, the exposed portion of the helical turns will move more than the portions next to the shield, and the helix will bend, deilecting its axis from the position shown by dotted line 9, to the position shown by dotted line I0. 'Ihis will operate to bring the contacts 4 and 5 together, and close a circuit. To determine the direction of axial' movement, i. e., expansion or contraction, with temperature rise, the following rule can be observed: If the high expansion side `o1' the bimetal is on the inside of the minor helix, and both minor and major helices are wound with An element of this type the same direction of pitch, i. e., both left-hand This minor helix is then wound as a.

' screw or both right hand,

the major helix will contract on `being heated. If the minor and major helices are wound on opposite screws, i. e., one left, and the other right, the major helix will expand on being heated. On the other hand, if the high expansion side is on the outside of the minor helix, the opposite is true, that is; same screw-expands on heating; opposite screw-contracts on heating. To determine the direction of bending movement when one side of the major helix is heated more than the other side, the following rule can be observed: If the major' helix is so wound that it expands axially when its whole body is heated, then if only one side is heated, the free end of the major helix (assuming one end is fastened) will bend toward the heated side. Ifthe major helix is so wound as to contract axially when its whole body is heated, then the free end will bend away from the heat. For example, in Figure 2, the major helix is so wound that it contracts on heating. Then when the portion of it not surrounded by the shield is heated, the free end 4 bends toward the stationary contact 5. It will be clear, of course, that by reversing the position of the layer of relatively high expansion and that of relatively low expansion or by otherwise properly changing the direction of axial movement of the major helix, the helix will curve in the opposite directionas the temperature rises, and if the contacts are closed when the thermostat is in the Fig. 2 position, they will open as it responds to a rapid increase intemperature.

An alternative embodiment is shown in Figures 4, 5 and 6. Here the shield 3 is present as before, but the device is operated by means of a heating Wire II, located on the side of the helix opposite the shield 3. Movable contact 4 is as described above, but stationary contact I2 is made in the form of a long bar. Heating wire I I is conveniently supported on member 30 which is insulated from the controlled circuit. Gradual changes in ambient temperature will cause the helix to expand or contract in a horizontal direction, leaving the contacts 4 and I2 unaffected. However, the application of current to heating wire II will cause the helix to bend in an ap-l .propriate direction, as indicated in Fig. 5, where the axis of the helix is shown passing into the curved line I3 fromthe straight line I4 position. The Fig. 5 switch is adapted to close a circuit upon the passage of currentthrough the heating wire II'. By reversing the positions of the layers of bimetal, or by otherwise properly changing the direction of axial movement of the major helix, the switch may be caused to open upon passage of current through this heating wire II.

Figures '1, 8 and 9 show a still different embodiment of the presentinvention.- Here the helix 2 is mounted in operative association with a movable contact-carrying lever I5, which cooperates with a ixed contact I6. The lever I5 is mounted in turn on a rulcrum I1. The helix 2 on its opposite end, is in operative association with a simple coiled spring I8 through a movable plate I9. A pigtail isv conveniently employed to allow for the motion of the lever I5 when it operates. In this embodiment, a heater 2I is positioned adjacent to one side of the helix. As the ambient temperature changes gradually, the helix 2 will expand or contract. This expansion or contraction is absorbed by the spring Il, and its eiect is thus minimized on the-lever I5. However, upon the passage of substantial current through heater 2l, the center of the helix will bend away from the heat to the Fig. 8 position. As the center of pressure of the helix illustrated by line 3l passes the fulcrum I1, the lever I5 will snap open with an abrupt movement, breaking the contact. It is of course clear (as explained above) that by reversing the position of the high expansion and low expansion layers in the element, andby placing the fulcrum point initially on the left'of the axis line of the element, the device can be conveniently converted to a switch closing mechanism.

Fig. 10 villustrates a variation of the Fig. 7 embodiment. Here the iulerum 32 is floating, instead of being attached to the movable arm. The movable arm 33 has a valley 3l which cooperates with the fulcrum 32 to position the arm 33 to contact the stationary button II. 'I'he operation of this device is similar to that of the Fig. 7 embodiment.

Figures 11 and 12 illustrate a still further variation of the Fig. 1 embodiment of the invention. Here the bottom portion of the helix 2 is brought down in the form or a portion 35,'whi`ch is attached as by soldering or welding at 36, to the movable arm 31. The portion has an open- 38 adapted to receive a rod 39 which positions the movable arm 31 in relation to the relatively stationary contact 40. It will be understood of course that the rod 39 is held in suitable openings 4I in arms projecting upwardly from base.

Figures 11 and 12 likewise illustrate a preferred embodiment of the relatively stationary contact 40. -It will be noted that this contact is mounted upon a spring member 42 adapted to retain the contact I0 in cooperation with the arm 31 over a relatively limited area of movement. This eliminates any arcing caused by creeping of the thermostat prior to snapping the arm 31 out of contact with button I0. The operation of the Figures 11 and 12 `embodiment is analogous to that of the Fig. 'l embodiment.

` From the foregoing description, it will be apparent that the present invention provides a simple, economically constructed switch, which is sensitive to rate of change of temperature. This device moreover, requiresvonly one thermostatic element. It may be conveniently employed for any of the usual purposes, such as opening or closing a circuit in a motor protection device, flre alarm, to operate wa valve, or for other purposes where it is desired that the thermostat shall be independent of slowly changing ambient temperature, but responsive to rate-of-change of temperature. Moreover, the embodiment shown in Figures 7-12 operate with a snap action, thus avoiding or reducing arcing between the contacts and thereby prolonging their life.

In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.

As many changes could be made in the above constructions without departing from the scope 'of the invention, it is intended that all matter contained in the above description or shownv in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

coil composed of a strip of composite metal and f means for locally heating the coil. g

5. A thermostatic element comprising strips o1' metal of diierent coeiiicients of thermal expansion rigidly connected along their length and extending progressively about a first axis, which in turn is extended progressively about a second axis, and means for causing one portion of the element to respond more rapidly to temperature change than another portion.

6. A thermostat comprising a helix composed of a coiled strip of composite metal and means comprising a shield for causing one portion of the helix to respond more rapidly to temperature change than another.

7. A thermostat comprising a helix composed of a coiled strip of composite metal and means comprising a heating element for causing onev portion of the helix to respond more rapidly to temperature change than another portion.

8. A thermostat comprising a helix composed of a coiled strip of composite metal, a xed contact, a movable contact mounted onya fulcrum and located in operative relationship to said helix, and means for causing one portion of the helix to respond more rapidly to temperaturel change than another portion.

9. An article of manufacture comprising a bimetallic helix of axially elongated form comprising a succession of axially progressing coils, at least one of which has at least one loop about an axis transversel with respect to the axis of said coils, and means for causing one portion of the helix to respond more rapidly to temperature change than another portion. A

1,0. A thermostatic element comprising strips of metal of. diierent coemcients o1' thermal expansion rigidly connected along their length and extending progressively about a rst axis, which in turn is extended progressively about a second axis, and means comprising a shield for causing one portion of the'element to respond more rapidly to temperature change than another portion. l1. A thermostatic element comprising strips of metal of dilerent coeilicients of thermal expansion rigidly connected along their length and extending progressively about a rst axis, which in turn is extended progressively about a second axis, and means comprising a heating element forcausing one portion of the element to respond temperature change than another-portion.

12;;.A thermostatic element comprising strips of metal of diierent coefllcients oi thermal expansion rigidly connected along their length and extending progressively about a rst axis,- which in turn is extended progressively about a second axis, a fixed contact, a movable contact mounted on a fulcrum and located in operative relationl:hip to said element, and means for causing che portion of the element to respond more rapprising a succession of axially progressing coils, at least one of which has at least one loop about an axis transverse with respect to the axis of said coils, and means comprising a shield for causing one portion of the helix to respond more rapidly to temperature change than another portion.

14. An article of manufacture comprising a -bimetallic helix of axially elongated form comprising a succession of axially progressing coils, at least one of which has at least one loop about an axis transverse with respect to the axis of said coils, and means comprising a heating element for causing vone portion of the helix to respond more rapidly to temperature change than another.

15. An article of manufacture comprising a bimetallic helix of axially elongated form comprising a succession of axially progressing coils, at least one of which has at least one loop about an axis transverse with respect to the axis of said coils, a xed contact, a movable contact mounted on a fulcrum and located in operative relationship to said helix, and means for causing one portion of the helix to respond more rapidly to temperature change than another portion 16. A rate-oi'change thermostat comprising a compound helix of composite metal and means for locally heating one side of the helix.

17. A rate-of-change thermostat comprising a single compound helix of composite metal, said helix having axially directed movement in response to temperature change uniformly distributed about the periphery of the helix, and means for causing a differential temperature change of said periphery, whereby said helix undergoesy a movement at right angles to/ said axially directed movement.

18. A. rate-of-change thermostat comprising a single compound helix of composite metal, said helix having a movement in the direction of the axis of the helix when subjected uniformly to temperature change, and means for causing one portion of the helix to respond to temperature change more rapidly than another portion, whereby in response to said second change of temperature, said helix undergoes a motion in a direction at right angles to the axis of the helix.

19. An article of manufacture comprising a bimetallic helix oi axially elongated form ccmprising a succession of axially progressing coils, at least one of which has at least one loop about an axis transverse with respect to the axis of said coils, a lixed contact, a movable contact mounted on a fulcrum and attached to said helix, and means for causing one portion of the helix to respond more rapidly to temperature change than another portion.

20. An article of manufacture comprising a bimetallic helix of axially elongated form comprising a succession of axially progressing coils, at least one of which has at least one loop about an axis transverse with respect to the axis of said coils, a relatively iixed contact mounted upon a spring member, a movable contact mounted onfa ulcrum and located in operative relationshipl to -said helix, and means' for causing one portion of the helix to respond more rapidly to temperature change than another portion.

wALDo A. SAUL. 

